1. Field of the Invention
The present invention relates to a semiconductor storage device and a manufacturing method therefor. More particularly, the present invention relates to a semiconductor storage device which uses a ferroelectric capacitor formed by sandwiching a ferroelectric material between electrodes and a manufacturing method therefor.
2. Description of the Related Art
A ferroelectric material, that is a material having a spontaneous polarization that can be inverted by electric field (ferroelectric domain inversion) has been studied and proposed to be used for a semiconductor storage device. A ferroelectric memory, using a ferroelectric capacitor where a thin film of ferroelectric material is sandwiched between an upper electrode and a lower electrode, has already been developed.
This ferroelectric material memory is composed of a ferroelectric material capacitor and a transistor unit. The ferroelectric capacitor is constructed from a thin ferroelectric film that is sandwiched between an upper electrode and a lower electrode, made with metal having a high melting point, such as Platinum (Pt) or the like. The transistor unit is formed on a silicon substrate by an original method. A direction connection or a direct contact via aluminum (Al) is generally used for an electric contact between the ferroelectric capacitor unit and the transistor unit.
On the other hand, it is known that frequent repetition of ferroelectric domain inversion deteriorates the characteristics of a ferroelectric thin film, which is the main material of the ferroelectric capacitor. This deterioration of characteristics is a phenomenon of the decrease in spontaneous polarization value, the so-called fatigue. This phenomenon is caused by an oxygen defect in the ferroelectric thin film contacting the electrode caused by the frequent repetition of ferroelectric domain inversion. When oxygen in the ferroelectric thin film becomes defective, a decrease of spontaneous polarization value is reported.
Pt, mainly used for the electrodes, is catalytically active. This Pt accelerates damage to the ferroelectric thin film by nascent hydrogen during the semiconductor processes. The nascent hydrogen of an interlayer dielectric is formed or a sinter that increases a transistor characteristic deoxidizes the ferroelectric material and deteriorates the characteristic of the ferroelectric material.
To prevent the deterioration-described above, material for the upper electrode of the ferroelectric capacitor should be carefully selected. Recently, material catalytically inactive has been selected for the material of the upper electrode. Furthermore, conductive oxide material containing oxygen has been selected for the upper electrode.
By selecting a conductive oxide material containing oxygen, damage by hydrogen in the subsequent processes can be prevented. On the other hand, oxygen provided from the conductive oxide electrode to the ferroelectric thin film compensates the oxygen in the ferroelectric thin film defected by the frequent ferroelectric domain inversion and the undesirable fatigue of the characteristics can be improved.
It is difficult to form a connection between the oxide electrode and a diffusion layer of silicon substrate with the Al material. It was normally necessary to form a Ti film above the diffusion layer in order for good contact to be formed between the Al material and the diffusion layer of the silicon substrate. It is necessary to form a Ti film for a few ten nm thicknesses above the diffusion layer using a sputter method or the like. The Ti film is naturally formed on the upper oxide electrode as well. This Ti film is characteristically easy to oxidize. Application of a rapid heat treatment is required after the formation of the Ti film. This heat treatment causes the Ti film to react with the oxide material electrode and form a TiOX film, which is an insulator. This TiOX film can cause a loose connection. Moreover, when the Ti film is oxidized and TiOX is formed, it expands to twice the volume of the original Ti film. Adhesion between the Ti film and the conductive oxide electrode deteriorates. When nitride Ti (TiN) and Al material is formed in subsequent processes, there is a problem that peeling of the Ti film will occur.
Therefore, it is an object of the present invention to provide a semiconductor storage device together with its manufacturing method which overcomes the above difficulties accompanying the conventional art.
To achieve the object described above, semiconductor storage device and its manufacturing method according to the first aspect of the present invention, a semiconductor storage device includes a lower electrode made of a high melting point metal, an upper electrode made of conductive oxide, a ferroelectric capacitor made of a ferroelectric material film sandwiched between the lower electrode and the upper electrode, and a switching transistor, characterized in that a TiN film is formed between the upper electrode and a wiring electrode. The lower electrode may be made of Pt. The upper electrode may be made of one of SrRuO, IrO2, RuO2, and LaSrCoO. A Ti film may be formed between the wiring electrode and the TiN film.
A method of manufacturing a semiconductor storage device according to an aspect of the present invention, includes steps of: forming a first insulation film on a semiconductor substrate on which a switching transistor is formed; depositing a high melting point metal film, a ferroelectric material film, and an oxide conductive material film sequentially; forming an upper electrode by patterning the oxide conductive material film; patterning the ferroelectric material film and the high melting point metal film; forming a contact hole to the lower electrode by patterning the ferroelectric material film; forming a resist pattern after forming a second insulation film; exposing a part of the upper electrode and the lower electrode by etching the second insulation film to form an opening, using the resist pattern as a mask; forming TiN film on the substantially the whole surface; and selectively remaining the TiN film, only on the part exposed by the opening, by removing the resist pattern.
Another method of manufacturing a semiconductor storage device according to another aspect of the present invention, includes steps of: forming a first insulation film on a semiconductor substrate on which a switching transistor is formed; depositing a high melting point metal film, a ferroelectric film, and an oxide conductive material film sequentially; forming an upper electrode by patterning the oxide conductive material film; patterning the ferroelectric material film and the high melting ponit metal film; forming a contact hole to the lower electrode by patterning the ferroelectric material film; forming a resist pattern after forming a second insulation film then; exposing a part of the diffusion layer of the switching transistor by etching the second insulation film and the first insulation film to form an opening, using the resist pattern as a mask; forming Ti film substantially on the whole surface; selectively remaining Ti film remains, only on the exposed part of the opening, by removing the resist pattern; forming an opening to expose a part of the upper electrode and the lower electrode on the second insulation film; and forming TiN film above the exposed upper electrode and the exposed lower electrode.
Furthermore, another method of manufacturing a semiconductor storage device according to the other aspect of the present invention, includes steps of: forming a first insulation film on a semiconductor substrate on which a switching transistor is formed; depositing a high melting point metal film, a ferroelectric material film, and an oxide conductive material film sequentially; patterning the TiN film and oxide conductive material film at the same time to form an upper electrode; patterning the ferroelectric material film and the high melting point metal film; forming a contact hole to lower electrode by patterning the ferroelectric material film; forming a resist pattern after forming a second insulation film; exposing a part of the upper electrode and the lower electrode, and a part of diffusion layer of the switching transistor by etching the second insulation film to form an opening, using the resist pattern as a mask; and forming Ti film and wiring metal film on substantially the whole surface sequentially and patterning the films.
The lower electrode may be made of Pt. The upper electrode is made of one of SrRuO, IrO2, RuO2, and LaSrCoO. The wiring electrode film is made of Al alloy.
This summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the above described features. The above and other features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings.